• 한국농공학회논문집
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• 제48권7호
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• pp.35-43
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• 2006

This study was carried out to investigate the liquefaction behaviour and predict deviator stress with matric suction, of unsaturated silty sand. The unsaturated soil tests were conducted using a modified triaxial cell and specimens were prepared using the moisture tamping method. The axis translation technique was used to create the desired matric suctions in the specimen. Undrained triaxial compression tests were carried out at matric suction of 0, 2, 5, 10 and 25 kPa. The specimens were sheared to axial strains of about 20% to obtain steady state conditions. The results showed that liquefaction of silty sand only occurs at matric suction of 0 kPa and 2 kPa. The results also show that at matric suctions of 5, 10 and 25 kPa, the resistance to liquefaction increases. As the suction increases, the undrained effective stress path approached the drained stress path. Also, the predicted and measured maximum deviator stress for unsaturated soils using the effective stress concept showed good agreement as matric suction increases. The deviator stress increase is nonlinear as matric suction increases.

• Geomechanics and Engineering
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• 제18권5호
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• pp.459-469
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• 2019

It is important to estimate the shear strength of shallow compacted soils as a construction material. A series of constant water content triaxial compression (CWCC) tests under low confining state in this study were performed on compacted geomaterials. For establishing a relationship of the shear strengths between saturated and unsaturated states on compacted geomaterials, the suction stresses were derived by two methods: the conventional suction-measured method and the Suction stress-SWRC Method (SSM). Considering the suction stress as an equivalent confining stress component in the (${\sigma}_{net}$, ${\tau}$) plane, it was found that the peak deviator stress states agree well with the failure line of the saturated state from the triaxial compression test when the SSM is applied to obtain the suction stress. On the other hand, the cavitation phenomenon on the measurement of suction affected the results of the conventional suction-measured method. These results mean that the SSM is distinctly favorable for obtaining the suction value in the CWCC test because the SSM is not restricted by the cavitation phenomenon. It is expected that the application of the SSM would reduce the time required, and the projected cost with the additional equipment such as a pore water measuring device in the CWCC test.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회
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• pp.764-771
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• 2010

The stability analysis method of an unsaturated slope considering the suction stress was performed on the infinite sand slope. During drying and wetting processes, the Soil-Water Characteristics Curve (SWCC) of the sand with the relative density of 75% was measured using the automated SWCC apparatus. Also, the Suction Stress Characteristics Curve (SSCC) was estimated. Based on these results, the stability analysis of an unsaturated infinite slope was carried out considering the slope angle, the weathering zone and the relative change in friction angle as a soil depth. According to the result of slope stability analysis, the safety factors of slope were less than 1 when the slope angles were more than $50^{\circ}$. The safety factors of slope tend to increase with increasing the depth from the ground surface. Especially, the safety factors have a tendency to increase and decrease above near the ground water level due to the suction stress. The maximum safety factor of slope in this analysis was occurred at the Air Entry Value (AEV) of drying process. The influence range of suction stress above the ground water level can be found out and can be defined as the funicular zone which means the metric suction range from the air entry point to the point of residual volumetric water content.

• 한국지반공학회논문집
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• 제29권8호
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• pp.15-25
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• 2013

본 연구에서는 다짐된 편마풍화토의 불포화토 전단강도특성을 규명하기 위하여, Constant Water Content Compression (CWCC) 시험을 실시하였다. 두 가지 상대밀도로 구분하여 정적 다짐으로 공시체가 제작되었고, 초기 포화도를 변화시킴으로써 초기 흡수력 및 최대전단강도가 구현될 때의 흡수력에 따른 전단거동을 살펴보았다. 흡수력은 세라믹디스크와 간극수압계의 설치에 의해 직접 측정되었고, 이 흡수력을 적용하여 흡수응력(ps)이 추정되었다. CWCC 시험에서 얻어진 최대압축강도에 대한 결과는 삼축압축시험에서의 포화상태 파괴선(Mp Line)과의 관계, 즉 흡수력에 의해 발현된 전단강도의 변화를 흡수응력을 이용하여 살펴보았다. 또한, Kim 등(2010)이 제안한 Suction stress-SWCC Method (SSM)을 활용하여 흡수응력의 적용성에 대해 논하였다.

• Geomechanics and Engineering
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• 제25권4호
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• pp.283-294
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• 2021

This paper presents a rigorous solution for spherical cavity expansion in unsaturated soils under constant suction condition. The hydraulic behavior that describes the saturation-suction relationship is modeled by a void ratio-dependent soil-water characteristic curve, which allows the hydraulic behavior to fully couple with the mechanical behavior that is described by an extended critical state soil model for unsaturated soil through the specific volume. Considering the boundary condition and introducing an auxiliary coordinate, the problem is formulated to a system of first-order differential equations with three principal stress components and suction as basic unknowns, which is solved as an initial value problem. Parameter analyses are conducted to investigate the effects of suction and the overconsolidation ratio on the overall expansion responses, including the pressure-expansion response, the distribution of the stress components around the cavity, and the stress path of the soil during cavity expansion. The results reveal that the expansion pressures and the distribution of the stress components in unsaturated soils are generally higher than those in saturated soils due to the existence of suction.

• Geomechanics and Engineering
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• 제29권1호
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• pp.1-11
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• 2022

A semi-analytical solution to responses of overconsolidated (OC) unsaturated soils surrounding an expanding spherical cavity under constant suction condition is presented. To capture the elastoplastic hydro-mechanical property of OC unsaturated soils, the unified hardening (UH) model for OC unsaturated soil is adopted in corporation with a soil-water characteristic curve (SWCC) and two suction yield surfaces. Taking the specific volume, radial stress, tangential stress and degree of saturation as the four basic unknowns, the problem investigated is formulated by solving a set of first-order ordinary differential equations with the help of an auxiliary variable and an iterative algorithm. The present solution is validated by comparing with available solution based on the modified Cam Clay (MCC) model. Parametric studies reveal that the hydraulic and mechanical responses of spherical cavity expanding in unsaturated soils are not only coupled, but also affected by suction and overconsolidation ratio (OCR) significantly. More importantly, whether hydraulic yield will occur or not depends only on the initial relationship between suction yield stress and suction. The presented solution can be used for calibration of some insitu tests in OC unsaturated soil.

• 한국지반신소재학회논문집
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• 제10권3호
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• pp.25-32
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• 2011

본 연구에서는 자동 흙-함수특성곡선 시험장치를 이용하여 새만금지역에서 채취한 준설토의 모관흡수력과 체적함수비를 측정하였다. 측정결과를 토대로 Van Genuchten(1980)의 방법을 이용하여 흙-함수특성곡선(SWCC)을 산정하였다. 동일한 유효포화도에서 건조과정의 모관흡수력은 습윤과정의 모관흡수력보다 크게 나타났다. Lu and Likos(2006)의 방법을 이용하여 모관흡수력에 따른 흡입응력을 산정하고, 흙-함수특성곡선(SWCC)의 불포화 관련계수를 토대로 흡입응력특성곡선(SSCC)을 예측하였다. 건조과정의 흡입응력은 유효포화도가 증가함에 따라 증가하다가 감소하지만 습윤과정의 흡입응력은 유효포화도가 증가함에 따라 지속적으로 감소한다. 또한 동일한 유효포화도에서 건조과정의 흡입응력은 습윤과정의 흡입응력보다 크게 나타났다. 한편 van Genuchten(1980)의 방법을 이용하여 투수계수함수(HCF)를 예측하였다. 체적함수비가 증가함에 따라 불포화 투수계수는 증가하며, 동일한 모관흡수력에서 건조과정의 투수계수가 습윤과정의 투수계수보다 크게 나타났다. 흙-함수특성곡선(SWCC)과 흡입응력특성곡선(SSCC)의 산정결과에 의하면 건조 및 습윤과정에서 흡입응력 혹은 모관흡수력에 대한 이력현상이 발생되었다. 이러한 이력현상은 흙입자 사이의 간극수로 인한 잉크병 효과에 의한 것이다.

• 한국지반공학회논문집
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• 제21권5호
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• pp.143-151
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• 2005

본 연구는 불포화토의 역학적 특성, 특히 메트릭 흡인력(matric suction)을 이용하여 다짐토의 압밀 항복응력을 산정하는 방법에 대해 검토되었다. 이를 위해, 두 종류의 시험을 실시하였다. 하나는 흡인력을 측정하기 위하여 정적 다짐시험이 실시하였으며, 다른 하나는 수침시키지 않은 다짐토의 압밀시험을 실시하였다. 그 시험 결과, 다짐곡선 상에 흡인력의 분포를 나타낼 수 있었으며, 압밀시험에서 간극비의 변화는 흡인력에 의존하는 것을 알 수 있었다. 이상의 시험결과를 기초로 하여, 다짐 곡선을 포함하는 다짐토의 압밀 항복 응력을 산정하는 새로운 방법을 제안하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.121-128
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• 2005

This paper introduces a method of predicting the behavior of compacted soil with an unsaturated soil mechanics by considering the effect of suction as an increasing consolidation yield stress. Two kinds of experiments were conducted. One is a series of static compaction tests to monitor the suction, and the other is a series of compression tests on compacted soil without soaking. The results of our tests indicate that it is possible to derive the distribution of suction on compaction curves and to hypothesize the changes in void ratio in the compression tests that depends on the suction. In addition, a new method is proposed to estimate the consolidation yield stress of compacted soil with a simple chart including compaction curves.

• 한국농공학회지
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• 제40권5호
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• pp.37-42
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• 1998

This study was performed to evaluate the characteristics of volume change is unsaturated clayed soil. The medium-plastic clay was selected and compacted by 50% of Proctor standard compaction energy at 6% higher moisture content than its OMC. A series of isotropic compression tests and triaxial shear tests were performed. The results of the study are summarized as follows. At each matric suction, when the matric suction was increased, the yield stress was increased and slope of volume change was decreased. The more net mean stress was, the less the quantity of volume change was. In shear test, the volumetric strain was much rapidly changed in large matric than in low matric suctions. But the effect of matric suction to volume change disappeared under high net mean stress. At lower deviator stress the more matric suction was, the higher volume change was. But As the matric suction was increasing, the behavior of the unsaturated clayey soil was similar to that of saturated clayey soil. Volume change in the unsaturated clayey soil can be represented as a unique plane in three-dimensional space, which is the axes of net mean stress, matric suction and void ratio.